Currently, silicon is typically used as a semiconductor that is widely industrially used as a device for an integrated circuit (IC) and a large-scale integrated circuit (LSI). A silicon single crystal used in the semiconductor industry and the like is manufactured from polycrystalline silicon as raw materials by the floating zone melting method (FZ method for short) in which the bar-shaped polycrystalline silicon is melted by induction heating and a single crystal is grown, or by the Czochralski method (CZ method for short) in which the polycrystal is heated and melted in a crucible, a seed crystal is immersed in a melt and withdrawn therefrom, and a single crystal ingot is grown below the seed crystal.
A manufacturing method is selected from these methods in accordance with usage of the single crystal. In general, a single crystal manufactured by the FZ method is used for high resistivity and a single crystal manufactured by the CZ method is used for low to moderate resistivity.
In recent years, reduction in parasitic capacitance is required in a semiconductor device for mobile communication and in a leading-edge C-MOS device. It is reported that signal loss in transmission and parasitic capacitance in Schottky barrier diode can be effectively reduced by using a substrate of high resistivity. Given this, a high resistivity silicon wafer manufactured by the floating zone melting method (FZ method) is used for manufacturing a power device such as a high-voltage power device, a thyristor or the like.
Meanwhile, in recent years, a large diameter silicon wafer is sought for improving performance and reducing cost of a semiconductor device. Consequently, a large diameter FZ silicon single crystal of at least 150 mm in diameter is required, and thus development of a manufacturing method thereof has been awaited.
In a case of manufacturing a large diameter silicon single crystal, particularly of at least 150 mm in diameter, by the FZ method, a polycrystalline silicon material having a diameter of at least 140 mm is considered to be preferably used as a raw material ingot. For example, for manufacturing a silicon single crystal of 200 mm in diameter, a method using polycrystalline silicon having a diameter of at least 145 mm as a silicon raw material ingot is disclosed in Japanese Unexamined Patent Application Publication No. 2003-55089 (hereinafter referred to as Patent Document 1).
As described above, it is generally profitable to manufacture a silicon single crystal from a silicon raw material ingot with a diameter as large as possible, from a perspective of productivity and the like. However, since a silicon raw material ingot for polycrystalline silicon that is commercially available is manufactured by vapor phase growth, it is difficult to manufacture a large diameter polycrystalline silicon, particularly of at least 150 mm in diameter. In addition, polycrystalline silicon of a large diameter has a drawback of having a nonuniform grain boundary structure. Consequently, a problem of an extremely low yield is reported, in a case of manufacturing a silicon single crystal of 200 mm in diameter by the FZ method using a polycrystalline silicon raw material ingot of 160 mm in diameter, since a single manufacturing process by the FZ method cannot make a single crystal dislocation free and therefore the process must be repeated. Furthermore, polycrystalline silicon of a large diameter has another drawback of having a high unit cost.
On the other hand, an attempt is being made to manufacture an FZ silicon single crystal by using a large diameter CZ silicon crystal bar obtained by the CZ method (for example, see Japanese Unexamined Patent Application Publication No. 2005-281076 and 2005-306653, hereinafter referred to as Patent Documents 2 and 3).